Seals can be used in a variety of end-use applications. One demanding end-use application is with oil production equipment, e.g., such as that used for drilling subterranean formations. An example of such equipment includes rotary cone drill bits that are connected to drill string. In use, the drill string and bit body are rotated in the bore hole where high pressures and temperatures are encountered.
The total useful life of a drill bit in such severe environments is in the order of 20 to 200 hours for bits in sizes of about 6½ to 12¼ inch diameter at depths of about 5,000 to 20,000 feet that are operated at about 200 rpm. Useful lifetimes of about 65 to 150 hours are typical. However, the useful life of drill bits that are operated at higher revolutions such as 375 rpm, i.e., high-speed drill bits, is generally in the range of from about 20 to 50 hours. The shortened useful life is often due to the increased frictional heat produced in the bit caused by the increased operating speed.
When a drill bit wears out or fails as a bore hole is being drilled, it is necessary to withdraw the drill string for replacing the bit. The amount of time required to make a round trip for replacing a bit is essentially lost from the drilling operation. This time can become a significant portion of the total time for completing a well, particularly as the well depths become great. It is therefore quite desirable to maximize the service life of a drill bit in a rock formation. Prolonging the time of drilling minimizes the time lost in “round tripping” the drill string for replacing the bits. Replacement of a drill bit can be required for a number of reasons, including wearing out or breakage of the structure contacting the rock formation.
One reason for replacing the rock bits includes failure or severe wear of the journal bearings. These bearings are subject to high pressure drilling loads, high hydrostatic pressures in the hole being drilled, and high temperatures due to drilling, as well as elevated temperatures in the formation being drilled. Considerable development work has been conducted over the years to produce bearing structures and to employ materials that minimize wear and failure of such bearings.
The journal bearings are lubricated with grease adapted to such severe conditions. Such lubricants are an important element in the life of a rock bit. Pressure and temperature conditions in a drill bit can vary with time as the drill bit is used. For example, when a “joint” of pipe is added to the drill string, weight on the bit can be relieved and slight flexing can occur. Such variations can result in “pumping” of the grease through O-ring seals, leading to loss of grease or introduction of foreign abrasive materials, such as drilling mud, that can damage bearing surfaces. Bearing failure can often be traced to failure of the seal that retains lubricant in the bearing. Lubricant may be lost if the seal fails, or if abrasive particles of rock work their way into the bearing surfaces, causing excessive wear.
Rock bit O-rings are expected to perform in environments that are extremely harsh. Modern bits are being run at exceptionally high surface speeds, sometimes more than 500 feet per minute, with cone speeds averaging in the range of from 200 to 400 revolutions per minute. One face of the O-ring is exposed to abrasive drilling mud. The life of the O-ring may be significantly degraded by high temperatures due to friction (as well as elevated temperature in the well bore) and abrasion.
It is therefore desired that a seal have a material construction that is capable of maintaining the lubricant within oil production equipment, e.g., a drill bit, that has a long useful life, that is resistant to crude gasoline and other chemical compositions found within oil wells, that has high heat resistance, is resistant to abrasion, and that will not readily deform under load and allow leakage of the grease from within the bit or drilling mud into the bit, thereby providing a desired improvement in service life when compared to seals formed from conventional elastomeric materials.